User's Manual

Using GPS
30 GeoExplorer 2005 Series Getting Started Guide
Note – All accuracy figures are for both real-time and postprocessed
differentially corrected positions, unless otherwise stated.
In addition, the GeoXH handheld enables you to use H-Star
technology to provide to obtain 30 cm (subfoot) postprocessed
accuracy for static GPS positions. Using an external Zephyr antenna,
the GeoXH receiver is capable of providing postprocessed accuracy of
20 cm (8 inches) or better for static GPS positions.
Note – Accuracy estimates for streaming (dynamic) GPS positions may
be larger than 20 cm (using the external Zephyr antenna) or 30 cm
(using the internal antenna).
Factors that affect accuracy
As discussed above, the accuracy that you obtain from your
GeoExplorer 2005 series handheld is affected by the receiver model,
the type of antenna used, whether the data is differentially corrected
in real-time or after data collection, and whether you are logging a
point feature using static GPS positions, or a line or area feature using
streaming GPS positions.
The table below lists several other factors that affect the accuracy
obtained from your receiver, and recommends ways to minimize
their effect.
Factor Description To Maximize Accuracy
Number of
visible
satellites
The accuracy of your data
increases with the number of
satellites being used to
calculate the position.
You need at least four satellites to
calculate an accurate 3-dimensional
position. Trimble data collection
software only logs GPS positions when
four or more satellites are visible.
Tracking more satellites can help to
lower DOP values.
Multipath Multipath is when GPS
satellite signals are reflected
off nearby objects, such as
buildings or cars, causing an
erroneous signal to be
received by the GPS antenna.
This can cause errors of several
meters.
To reduce multipath, collect data in an
open environment away from large
reflective surfaces and with a clear
view of the sky. In high multipath
environments, record velocity data and
use velocity filtering when
postprocessing the data.